实验2
实验任务1:
源代码T.h
1 #pragma once 2 #include<string> 3 4 class T{ 5 public: 6 T(int x=0,int y=0); 7 T(const T &t); 8 T(T &&t); 9 ~T(); 10 11 void adjust(int ratio); 12 void display() const; 13 14 private: 15 int m1,m2; 16 17 public: 18 static int get_cnt(); 19 20 public: 21 static const std::string doc; 22 static const int max_cnt; 23 24 private: 25 static int cnt; 26 27 friend void func(); 28 }; 29 30 void func();
源代码T.cpp
1 #include "T.h" 2 #include<iostream> 3 #include<string> 4 5 const std::string T::doc { 6 "a simple class sample" 7 }; 8 const int T::max_cnt=999; 9 int T::cnt=0; 10 11 int T::get_cnt() { 12 return cnt; 13 } 14 15 T::T(int x,int y):m1 {x},m2 {y} { 16 ++cnt; 17 std::cout << "T constructor called.\n"; 18 } 19 20 T::T(const T &t):m1{t.m1},m2{t.m2}{ 21 ++cnt; 22 std::cout << "T copy constructor called.\n"; 23 } 24 25 T::T(T &&t):m1{t.m1},m2{t.m2}{ 26 ++cnt; 27 std::cout << "T move constructor called.\n"; 28 } 29 30 T::~T(){ 31 --cnt; 32 std::cout << "T destructor called.\n"; 33 } 34 35 void T::adjust(int ratio){ 36 m1*=ratio; 37 m2*=ratio; 38 } 39 40 void T::display() const { 41 std::cout << "(" << m1 << "," << m2 << ")"; 42 } 43 44 void func(){ 45 T t5(42); 46 t5.m2=2049; 47 std::cout << "t5 = "; 48 t5.display(); 49 std::cout << '\n'; 50 }
源代码task1.cpp
1 #include "T.h" 2 #include<iostream> 3 4 void tset_T(); 5 6 int main(){ 7 std::cout << "tset class T:\n"; 8 tset_T(); 9 10 std::cout << "\ntest fried func:\n"; 11 func(); 12 } 13 14 void test_T(){ 15 using std::cout; 16 using std::endl; 17 18 cout << "T info: " << T::doc << endl; 19 cout << "T objects'max count: " << T::max_cnt << endl; 20 cout << "T objects'current count: " << T::get_cnt() << endl << endl; 21 22 T t1; 23 cout << "t1 = ";t1.display();cout << endl; 24 25 T t2(3,4); 26 cout << "t2 = ";t2.display();cout << endl; 27 28 T t3(t2); 29 t3.adjust(2); 30 cout << "t3 = ";t3.display();cout << endl; 31 32 T t4(std::move(t2)); 33 cout << "t4 = ";t4.display();cout << endl; 34 35 cout << "test:T objects'current count: " << T::get_cnt() << endl; 36 }
运行结果截图：
问题1：
YES.类内的友元声明不替代函数的全局声明，去掉 line36 后，全局作用域中无 func 的原型声明，调用时编译器无法识别该函数。Dev-C++没有报错，是编译器兼容性的宽松处理。
问题2：
普通构造函数：
功能：初始化类 T 的对象，为成员变量分配初始值。
调用时机：当创建类 T 的对象时自动调用。
复制构造函数：
功能：用已存在的类 T 对象，拷贝其数据来初始化新的类 T 对象。
调用时机：用一个对象初始化另一个新对象。
移动构造函数：
功能：“窃取”右值对象（ t ）的资源，来初始化新的类 T 对象。
调用时机：用右值对象初始化新对象时。
析构函数：
功能：对象生命周期结束时，释放对象占用的资源。
调用时机：局部对象离开其作用域时；程序结束时，全局/静态对象被销毁时。
问题3：
程序不能正确编译，会出现重复定义错误。但是Dev-C++没报错，是因为当前项目中只包含了一个.cpp文件，没有多个文件重复包含T.h，所以没触发“重复定义”的链接错误。
实验任务2：
源代码Complex.h
1 #pragma once 2 #include<string> 3 4 class Complex{ 5 public: 6 static const std::string doc; 7 Complex(); 8 Complex(double Real); 9 Complex(double Real,double Imag); 10 Complex(const Complex &other); 11 Complex &operator=(const Complex &other); 12 double get_real()const; 13 double get_imag()const; 14 15 void add(const Complex &other); 16 17 friend void output(const Complex &c); 18 friend double abs(const Complex &c); 19 friend Complex add(const Complex &c1,const Complex &c2); 20 friend bool is_equal(const Complex &c1,const Complex &c2); 21 friend bool is_not_equal(const Complex &c1,const Complex &c2); 22 23 private: 24 double real,imag; 25 };
源代码Complex.cpp
1 #include "Complex.h" 2 #include<iostream> 3 #include<string> 4 #include<cmath> 5 6 const std::string Complex::doc { 7 "a simplified complex class" 8 }; 9 Complex::Complex():real(0.0),imag(0.0) {} 10 Complex::Complex(double Real):real(Real),imag(0.0) { 11 } 12 Complex::Complex(double Real,double Imag):real(Real),imag(Imag) { 13 } 14 Complex::Complex(const Complex &other):real(other.real),imag(other.imag) { 15 } 16 Complex &Complex::operator=(const Complex &other) { 17 if(this!=&other) { 18 real=other.real; 19 imag=other.imag; 20 } 21 return *this; 22 } 23 double Complex::get_real()const { 24 return real; 25 } 26 double Complex::get_imag()const { 27 return imag; 28 } 29 void Complex::add(const Complex &other){ 30 real+=other.real; 31 imag+=other.imag; 32 } 33 void output(const Complex &c){ 34 std::cout << c.real; 35 if(c.imag>=0){ 36 std::cout << "+" << c.imag << "i"; 37 } 38 else if(c.imag<0){ 39 std::cout << "-" << -c.imag << "i"; 40 } 41 } 42 double abs(const Complex &c){ 43 return sqrt(c.real*c.real+c.imag*c.imag); 44 } 45 Complex add(const Complex &c1,const Complex &c2){ 46 Complex result; 47 result.real=c1.real+c2.real; 48 result.imag=c1.imag+c2.imag; 49 return result; 50 } 51 bool is_equal(const Complex &c1,const Complex &c2){ 52 return c1.real==c2.real&&c1.imag==c2.imag; 53 } 54 bool is_not_equal(const Complex &c1,const Complex &c2){ 55 return !is_equal(c1,c2); 56 }
源代码task2.cpp
1 // 待补足头文件 2 3 #include "Complex.h" 4 #include <iostream> 5 #include <iomanip> 6 #include <complex> 7 8 void test_Complex(); 9 void test_std_complex(); 10 11 int main() { 12 std::cout << "*******测试1: 自定义类Complex*******\n"; 13 test_Complex(); 14 15 std::cout << "\n*******测试2: 标准库模板类complex*******\n"; 16 test_std_complex(); 17 } 18 19 void test_Complex() { 20 using std::cout; 21 using std::endl; 22 using std::boolalpha; 23 24 cout << "类成员测试: " << endl; 25 cout << Complex::doc << endl << endl; 26 27 cout << "Complex对象测试: " << endl; 28 Complex c1; 29 Complex c2(3, -4); 30 Complex c3(c2); 31 Complex c4 = c2; 32 const Complex c5(3.5); 33 34 cout << "c1 = "; output(c1); cout << endl; 35 cout << "c2 = "; output(c2); cout << endl; 36 cout << "c3 = "; output(c3); cout << endl; 37 cout << "c4 = "; output(c4); cout << endl; 38 cout << "c5.real = " << c5.get_real() 39 << ", c5.imag = " << c5.get_imag() << endl << endl; 40 41 cout << "复数运算测试: " << endl; 42 cout << "abs(c2) = " << abs(c2) << endl; 43 c1.add(c2); 44 cout << "c1 += c2, c1 = "; output(c1); cout << endl; 45 cout << boolalpha; 46 cout << "c1 == c2 : " << is_equal(c1, c2) << endl; 47 cout << "c1 != c2 : " << is_not_equal(c1, c2) << endl; 48 c4 = add(c2, c3); 49 cout << "c4 = c2 + c3, c4 = "; output(c4); cout << endl; 50 } 51 52 void test_std_complex() { 53 using std::cout; 54 using std::endl; 55 using std::boolalpha; 56 57 cout << "std::complex<double>对象测试: " << endl; 58 std::complex<double> c1; 59 std::complex<double> c2(3, -4); 60 std::complex<double> c3(c2); 61 std::complex<double> c4 = c2; 62 const std::complex<double> c5(3.5); 63 64 cout << "c1 = " << c1 << endl; 65 cout << "c2 = " << c2 << endl; 66 cout << "c3 = " << c3 << endl; 67 cout << "c4 = " << c4 << endl; 68 69 cout << "c5.real = " << c5.real() 70 << ", c5.imag = " << c5.imag() << endl << endl; 71 72 cout << "复数运算测试: " << endl; 73 cout << "abs(c2) = " << abs(c2) << endl; 74 c1 += c2; 75 cout << "c1 += c2, c1 = " << c1 << endl; 76 cout << boolalpha; 77 cout << "c1 == c2 : " << (c1 == c2)<< endl; 78 cout << "c1 != c2 : " << (c1 != c2) << endl; 79 c4 = c2 + c3; 80 cout << "c4 = c2 + c3, c4 = " << c4 << endl; 81 }
运行结果截图：
问题1：
在使用形式上，标准库模板类 complex 更简洁。函数和运算内在有关联：标准库的运算本质是通过重载运算符函数实现的，只是语法形式更接近自然运算。
问题2：
2-1：是。output 需要输出 real / imag ， abs 需要计算 real²+imag² ， add 需要获取 real / imag 做加法——这些操作都依赖类的私有成员 real 和 imag ，因此需要设为友元来访问私有数据。
2-2：否。标准库 std::complex 的 abs 函数并非友元，而是通过类的公共接口获取实部、虚部后计算的。
2-3：函数/类需要访问当前类的私有/保护成员，且无法通过公共接口实现；实现不同类之间的协作。
问题3：
为 Complex 类添加拷贝构造函数。
实验任务3：
源代码PlayerControl.h
1 #pragma once 2 #include <string> 3 4 enum class ControlType {Play, Pause, Next, Prev, Stop, Unknown}; 5 6 class PlayerControl { 7 public: 8 PlayerControl(); 9 10 ControlType parse(const std::string& control_str); 11 void execute(ControlType cmd) const; 12 13 static int get_cnt(); 14 15 private: 16 static int total_cnt; 17 };
源代码PlayerControl.cpp
1 #include "PlayerControl.h" 2 #include <iostream> 3 #include <algorithm> 4 5 int PlayerControl::total_cnt = 0; 6 7 PlayerControl::PlayerControl() {} 8 9 // 待补足 10 // 1. 将输入字符串转为小写，实现大小写不敏感 11 // 2. 匹配"play"/"pause"/"next"/"prev"/"stop"并返回对应枚举 12 // 3. 未匹配的字符串返回ControlType::Unknown 13 // 4. 每次成功调用parse时递增total_cnt 14 ControlType PlayerControl::parse(const std::string& control_str) { 15 std::string lower_str=control_str; 16 std::transform(lower_str.begin(),lower_str.end(),lower_str.begin(),[](unsigned char c){ 17 return std::tolower(c); 18 }); 19 if(lower_str=="play"){ 20 total_cnt++; 21 return ControlType::Play; 22 } 23 else if(lower_str=="pause"){ 24 total_cnt++; 25 return ControlType::Pause; 26 } 27 else if(lower_str=="next"){ 28 total_cnt++; 29 return ControlType::Next; 30 } 31 else if(lower_str=="prev"){ 32 total_cnt++; 33 return ControlType::Prev; 34 } 35 else if(lower_str=="stop"){ 36 total_cnt++; 37 return ControlType::Stop; 38 } 39 else 40 return ControlType::Unknown; 41 } 42 43 void PlayerControl::execute(ControlType cmd) const { 44 switch (cmd) { 45 case ControlType::Play: std::cout << "[play] Playing music...\n"; break; 46 case ControlType::Pause: std::cout << "[Pause] Music paused\n"; break; 47 case ControlType::Next: std::cout << "[Next] Skipping to next track\n"; break; 48 case ControlType::Prev: std::cout << "[Prev] Back to previous track\n"; break; 49 case ControlType::Stop: std::cout << "[Stop] Music stopped\n"; break; 50 default: std::cout << "[Error] unknown control\n"; break; 51 } 52 } 53 54 int PlayerControl::get_cnt() { 55 return total_cnt; 56 }
源代码task3.cpp
1 #include "PlayerControl.h" 2 #include <iostream> 3 4 void test() { 5 PlayerControl controller; 6 std::string control_str; 7 std::cout << "Enter Control: (play/pause/next/prev/stop/quit):\n"; 8 9 while(std::cin >> control_str) { 10 if(control_str == "quit") 11 break; 12 13 ControlType cmd = controller.parse(control_str); 14 controller.execute(cmd); 15 std::cout << "Current Player control: " << PlayerControl::get_cnt() << "\n\n"; 16 } 17 } 18 19 int main() { 20 test(); 21 }
运行结果截图：
实验任务4：
源代码Fraction.h
1 #pragma once 2 #include<string> 3 4 class Fraction{ 5 public: 6 static const std::string doc; 7 Fraction(int up_v); 8 Fraction(int up_v,int down_v); 9 Fraction(const Fraction &other); 10 int get_up()const; 11 int get_down()const; 12 Fraction negative()const; 13 friend void output(const Fraction &f); 14 friend Fraction add(const Fraction &f1,const Fraction &f2); 15 friend Fraction sub(const Fraction &f1,const Fraction &f2); 16 friend Fraction mul(const Fraction &f1,const Fraction &f2); 17 friend Fraction div(const Fraction &f1,const Fraction &f2); 18 private: 19 int up,down; 20 void simplify(); 21 static int gcd(int a,int b); 22 };
源代码Fraction.cpp
1 #include "Fraction.h" 2 #include<iostream> 3 #include<stdexcept> 4 5 const std::string Fraction::doc="Fraction类 v 0.01版.\n目前仅支持分数对象的构造、输出、加/减/乘/除运算."; 6 int Fraction::gcd(int a,int b){ 7 a=abs(a); 8 b=abs(b); 9 while(b!=0){ 10 int temp=b; 11 b=a%b; 12 a=temp; 13 } 14 return a; 15 } 16 void Fraction::simplify(){ 17 if(down==0) 18 throw std::invalid_argument("分母不能为0！"); 19 if(down<0){ 20 up=-up; 21 down=-down; 22 } 23 int common_div=gcd(up,down); 24 if(common_div!=0){ 25 up/=common_div; 26 down/=common_div; 27 } 28 } 29 Fraction::Fraction(int up_v):up(up_v),down(1){ 30 simplify(); 31 } 32 Fraction::Fraction(int up_v,int down_v):up(up_v),down(down_v){ 33 simplify(); 34 } 35 Fraction::Fraction(const Fraction &other):up(other.up),down(other.down){ 36 } 37 int Fraction::get_up()const{ 38 return up; 39 } 40 int Fraction::get_down()const{ 41 return down; 42 } 43 Fraction Fraction::negative()const{ 44 return Fraction(-up,down); 45 } 46 void output(const Fraction &f){ 47 if(f.up==0) 48 std::cout << f.up; 49 else if(f.down==1) 50 std::cout << f.up; 51 else 52 std::cout << f.up << "/" << f.down; 53 } 54 Fraction add(const Fraction &f1,const Fraction &f2){ 55 int new_up=f1.up*f2.down+f2.up*f1.down; 56 int new_down=f1.down*f2.down; 57 return Fraction(new_up,new_down); 58 } 59 Fraction sub(const Fraction &f1,const Fraction &f2){ 60 int new_up=f1.up*f2.down-f2.up*f1.down; 61 int new_down=f1.down*f2.down; 62 return Fraction(new_up,new_down); 63 } 64 Fraction mul(const Fraction &f1,const Fraction &f2){ 65 int new_up=f1.up*f2.up; 66 int new_down=f1.down*f2.down; 67 return Fraction(new_up,new_down); 68 } 69 Fraction div(const Fraction &f1,const Fraction &f2){ 70 if(f2.up==0) 71 throw std::invalid_argument("分母不能为0！"); 72 int new_up=f1.up*f2.down; 73 int new_down=f1.down*f2.up; 74 return Fraction(new_up,new_down); 75 }
源代码task4.cpp
1 #include "Fraction.h" 2 #include <iostream> 3 #include<stdexcept> 4 void test1(); 5 void test2(); 6 7 int main() { 8 std::cout << "测试1: Fraction类基础功能测试\n"; 9 test1(); 10 11 std::cout << "\n测试2: 分母为0测试: \n"; 12 test2(); 13 } 14 15 void test1() { 16 using std::cout; 17 using std::endl; 18 19 cout << "Fraction类测试: " << endl; 20 cout << Fraction::doc << endl << endl; 21 22 Fraction f1(5); 23 Fraction f2(3, -4), f3(-18, 12); 24 Fraction f4(f3); 25 cout << "f1 = "; output(f1); cout << endl; 26 cout << "f2 = "; output(f2); cout << endl; 27 cout << "f3 = "; output(f3); cout << endl; 28 cout << "f4 = "; output(f4); cout << endl; 29 30 const Fraction f5(f4.negative()); 31 cout << "f5 = "; output(f5); cout << endl; 32 cout << "f5.get_up() = " << f5.get_up() 33 << ", f5.get_down() = " << f5.get_down() << endl; 34 35 cout << "f1 + f2 = "; output(add(f1, f2)); cout << endl; 36 cout << "f1 - f2 = "; output(sub(f1, f2)); cout << endl; 37 cout << "f1 * f2 = "; output(mul(f1, f2)); cout << endl; 38 cout << "f1 / f2 = "; output(div(f1, f2)); cout << endl; 39 cout << "f4 + f5 = "; output(add(f4, f5)); cout << endl; 40 } 41 42 void test2() { 43 using std::cout; 44 using std::endl; 45 46 Fraction f6(42, 55), f7(0, 3); 47 cout << "f6 = "; output(f6); cout << endl; 48 cout << "f7 = "; output(f7); cout << endl; 49 cout << "f6 / f7 = "; 50 try{ 51 Fraction result=div(f6,f7); 52 output(result); 53 }catch(const std::invalid_argument& e){ 54 cout << e.what(); 55 } 56 cout << endl; 57 }
运行结果截图：
问题：
选择友元。优点：可以直接访问类的私有成员，更符合数学运算的直观写法，代码可读性高。缺点：破坏了封装性。
实验总结：
本次实验学习了如何设计类，并正确使用类，友元函数。在进行验证性实验时要注意代码的正确性和规范性，敲代码时要仔细认真，否则容易因名称敲错或者其它小细节导致代码运行失败；构造函数时对于默认值处理方面，单参数构造函数必须显式初始化所有成员变量，否则会导致未定义行为。在进行实验任务4时就是因为未初始化down，导致其默认值为0，无法正确输出分数，运行结果出错。
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